pgbench: add --partitions and --partition-method options.
After this commit, I noticed fairywren is failing [1] with below symptoms:
pg_regress/strings LOG: statement: SELECT CAST(f1 AS char(10)) AS "char(text)" FROM TEXT_TBL;
2019-10-03 05:36:00.373 UTC [24272:43] LOG: server process (PID 23756) was terminated by exception 0xC0000028
2019-10-03 05:36:00.373 UTC [24272:44] DETAIL: Failed process was running: INSERT INTO INTERVAL_TBL (f1) VALUES ('badly formatted interval');
2019-10-03 05:36:00.373 UTC [24272:45] HINT: See C include file "ntstatus.h" for a description of the hexadecimal value.
2019-10-03 05:36:00.373 UTC [24272:46] LOG: terminating any other active server processes 2
On quick googling, it seems exception 0xC0000028 is related to windows stack corruption or something like that. I don't think it is related to this patch. It is also not clear that postgres code is at fault for this, so, let's wait for another run and see if it fails again.
